Abstract: A nuclear fuel assembly is constructed with fuel assembly components that are wire wrapped and positioned in hexagonal rings within a fuel assembly duct. The fuel assembly components positioned in an outermost ring of the fuel assembly are wire wrapped with a pitch that is shorter than fuel assembly components positioned at an interior ring of the fuel assembly. The shorter pitch at the outer ring of the fuel assembly increases pressure drop of a coolant fluid at the edge and corner subchannels and thereby reduces the temperature gradient across the fuel assembly, which provides a higher output temperature of the nuclear reactor without substantially increasing peak temperature of the fuel cladding.

Abstract: A fuel assembly includes full length fuel rods which contain a plutonium fissile (Puf) but do not contain a burnable poison, full length fuel rods which contain the fissile uranium and the burnable poison, and partial length fuel rods which contain Puf but do not contain the burnable poison in a channel box. The plutonium enrichment is decreased in an order of the full length fuel rods. The concentration of the burnable poison of the full length fuel rod is higher than the concentration of the full length fuel rod. In each side of a rectangular outermost periphery adjacent to the inner surface of the channel box in a horizontal cross-sectional view of the fuel assembly, two partial length fuel rods are adjacently disposed, and the full length fuel rod containing the burnable poison is disposed to be adjacent to each partial length fuel rod.

Abstract: A low-power nuclear reactor includes a housing and a reflector forming a reactor core. The core includes inner and outer primary tubes therein, arranged together as bayonet tubes and intended for circulating a coolant, and secondary tubes, accommodating elements of a control and protection system. The reactor further includes an intake chamber for coolant of a primary loop, and a discharge chamber for coolant of the primary loop, separated by a partition. The outer primary tubes are secured on the intake chamber's bottom, and the inner primary tubes are secured on the partition. Fuel assemblies are mounted in the inner primary tubes on suspensions, which are mounted on the discharge chamber's upper portion. The secondary tubes are sealed off from the intake and discharge chambers for the coolant of the primary loop, and an inter-tube space of the core is filled with a medium or material transparent to neutrons.

Abstract: A fuel assembly for a nuclear power boiling water reactor, including: a fuel channel defining a central fuel channel axis, fuel rods, each having a central fuel rod axis, at least 3 water channels for non-boiling water, each water channel having a central water channel axis and each water channel having a larger cross-sectional area than the cross-sectional area of (the average) fuel rod. The fuel rods comprise a first group of full length fuel rods and a second group of shorter fuel rods. The fuel assembly comprises at least 5 fuel rods which belong to said second group and which are positioned such that the central fuel rod axis of each of these at least 5 fuel rods is closer to the central fuel channel axis than any of the water channel axes of the water channels.

Abstract: Nuclear fuel assemblies include non-symmetrical fuel elements with reduced lateral dimensions on their outer lateral sides that facilitate fitting the fuel assembly into the predefined envelope size and guide tube position and pattern of a conventional nuclear reactor. Nuclear fuel assemblies alternatively comprise a mixed grid pattern that positions generally similar fuel elements in a compact arrangement that facilitates fitting of the assembly into the conventional nuclear reactor.

Abstract: A vacuum assembled along a centerline axis used to collect fissile material. The vacuum includes a housing having internal chamber, a top end having a top opening, a bottom end having a bottom opening, and a radial intake port opening. The vacuum includes a suction apparatus having an intake disposed at the intake opening and having a hose connection means for mating with a vacuum hose assembly. The suction apparatus also includes a flow-through fan disposed in the top opening. The fan intakes and exhausts the airflow in a direction parallel with the centerline axis. The suction apparatus also includes a container connection means disposed at the bottom opening for connecting an external container to bottom end of the housing. There is also provided a first cylindrical free space having a center point disposed along the centerline axis and a diameter passing through the center point.

Abstract: A duct for a nuclear fuel assembly includes a tubular body and an elongated member. The tubular body has a sidewall with an inner face and an outer face and is configured to contain nuclear fuel within a fuel region. The elongated member extends from the outer face along at least a portion of the fuel region and has a contact surface configured to stabilize the duct during operation of the nuclear fuel assembly.

Abstract: A tie rod for reinforcing a nuclear fuel assembly. The tie rod includes an outer, hollow tubular member that extends from above the top nozzle through the bottom nozzle of the fuel assembly and has an axially split lower tip with an enlarged end and an upper portion having a circumferential threaded region. An inner rod extends axially through the hollow of the outer tube and has a slightly enlarged tip which spreads the split tip of the outer tube to lock the split tip below the lower nozzle of the fuel assembly. A nut is turned down on the upper threaded portion of the outer hollow tube and staked in position to lock the tie rod in position.

Abstract: A sintered fuel pellet for a water nuclear reactor fuel rod including a peripheral wall extending along a central axis and two end faces. At least one of the end faces includes at least a first chamfer extending from the peripheral wall towards the central axis with a first non-zero slope with respect to a plane perpendicular to the central axis and a second chamfer extending from the first chamfer towards the central axis with a second non-zero slope with respect to a plane perpendicular to the central axis, wherein the first slope is different from the second slope.

Abstract: An improved grid for a nuclear reactor fuel assembly that has an egg-crate base grid as the primary support structure with each support cell of the base grid that supports a fuel rod having a lock-support sleeve that is rotatable within the support cell between a first and second orientation. In the first orientation the lock-support sleeve fits loosely within the support cell of the base grid and respectively, loosely receives the fuel rods that are loaded therein. The lock-support sleeves are then rotated to a second orientation that locks the fuel rods axially within the support cells.

Abstract: Disclosed are a fuel rod and a fuel bundle using the fuel rod. The fuel rod may include first enriched uranium in a boost zone of the fuel rod, wherein the boost zone may be arranged directly at a bottom of the fuel rod. The fuel rod may also include second enriched uranium in a second zone of the fuel rod, wherein the second zone is arranged over the boost zone. The fuel rod may also include natural uranium in a third zone of the fuel rod, wherein the third zone is arranged over the second zone. In this fuel rod, a percent of enrichment of the enriched uranium in the boost zone is at least one percent.

Abstract: A grid (13) for supporting nuclear fuel pencils (3) for a nuclear fuel assembly (1) comprising a peripheral belt (17), the peripheral belt (17) comprising on at least one of its edges (35, 37) guide fins (33) is disclosed. The edge (35, 37) of the peripheral belt (17) has between the adjacent guide fins (33) recesses (39) towards the inside of the grid (13). The invention is applicable, for example, to pressurized water reactors.

Abstract: A module including a casing extending in a longitudinal direction, a bundle of fuel rods encased in and supported by the casing and connector provided on the casing for connecting the casing side-by-side to the casing of at least one other module to obtain a nuclear fuel assembly having a channel box defined by the casings of the assembled modules and of larger cross-section than the casing of each of the assembled modules and a bundle of fuel rods of larger cross-section than that of each the assembled modules.

Abstract: A spacer for holding fuel rods includes cells formed by a sleeve having an upper edge and a lower edge and a number of abutment surfaces. The lower edge has a wave shape with wave peaks aligned with a respective one of the abutment surfaces, and wave valleys located between two adjacent ones of the abutment surfaces. The upper edge has a wave shape with wave peaks, which are aligned with a respective one of the abutment surfaces, and wave valleys located between two adjacent ones of the abutment surfaces. Each of the abutment surfaces extend from a respective one of the wave peaks of the upper edge to a respective one of the wave peaks of the lower edge. The sleeves abut each other in the spacer along respective connection areas to make the abutment surfaces rotatable with respect to a center point of the connection area.

Abstract: Example embodiments may include a nuclear fuel rod and/or segment design using fuel element spacers. Fuel element spacers may be placed at intervals within fuel rods and/or segments in order to manipulate operating characteristics of the fuel rods and/or segments and/or decrease consequences of fretting of the fuel rod and/or segment. Example methods may include using fuel rods and/or segments having fuel element spacing elements by adjusting intervals of the spacing elements so as to affect the mechanical, neutronic, and/or thermal properties of the fuel rod and/or segment.

Abstract: A rod assembly for a fuel bundle of a nuclear reactor may include an upper end piece, lower end piece and a plurality of rod segments attached between the upper and lower end pieces and to each other so as to form an axial length of the rod assembly. The rod assembly may include an adaptor subassembly provided at given connection points for connecting adjacent rod segments or a given rod segment with one of the upper and lower end pieces. The connection points along the axial length of the rod assembly may be located where the rod assembly contacts a spacer in the fuel bundle. One (or more) of the rod segments may include an irradiation target therein for producing a desired isotope when a fuel bundle containing one (or more) rod assemblies is irradiated in a core of the reactor.

Abstract: A fuel rod for a nuclear reactor includes the fuel rod having a first axial zone positioned proximate to a bottom end, a second axial zone positioned adjacent to the first axial zone in the intermediate region, and a third axial zone positioned proximate to a top end. The first axial zone has an enrichment greater than the second axial zone and the second axial zone has an enrichment greater than or equal to the third axial zone. Also includes fuel assemblies having a plurality of fuel rods and methods of designing and manufacturing of fuel rods and fuel assemblies.

Abstract: The invention pertains to a nuclear fuel assembly in a nuclear water reactor. The fuel assembly includes an array of a plurality of axially extending elongated tubular nuclear fuel elements having first and second closed ends and encapsulating a fissionable material axially along at least a portion of an interior volume thereof and an exterior of at least one of the fuel elements. The fuel elements include a cladding that extends substantially axially between the first and second closed ends. The exterior surface of the cladding is modified to include a surface texture varying axially in a prescribed pattern along at least a portion of an axial length of the cladding. The surface texture includes a plurality of ribs placed parallel to one another and circumferentially around one or more of the fuel elements. Each of the plurality of ribs has a specified height, width, and pitch between each of the plurality of ribs.

Abstract: Zirconium-based metal alloy compositions comprise zirconium, a first additive in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350° C. to 750° C., and a second additive having a solubility in zirconium over the temperature range extending from 350° C. to 750° C. At least one of a solubility of the first additive in the second additive over the temperature range extending from 350° C. to 750° C. and a solubility of the second additive in the first additive over the temperature range extending from 350° C. to 750° C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350° C. to 750° C. Nuclear fuel rods include a cladding material comprising such metal alloy compositions, and nuclear reactors include such fuel rods. Methods are used to fabricate such zirconium-based metal alloy compositions.

Abstract: A filter including a plurality of flow ducts extending in a longitudinal direction and each delimited between one pair of walls is provided. The filter includes deflectors protruding into each duct alternately from the pair of walls with overlapping in the longitudinal direction to define a zigzag shaped flow channel and provided with at least one set of holes aligned in the longitudinal direction to define through the overlapping deflectors a passage for accommodating a lower end pin of a fuel rod.

Abstract: The present invention relates to a nuclear reactor, in particular a pool-type nuclear reactor cooled with liquid metal (for example, a heavy metal such as lead or lead-bismuth eutectic) or with sodium or molten salts, having a core formed by a bundle of fuel elements and immersed in a primary fluid circulating between the core and at least one heat exchanger; the fuel elements extend along respective parallel longitudinal axes and have respective bottom active parts immersed in the primary fluid to constitute the core, and respective service parts that extend at the top from the active parts and emerge from the primary fluid; the fuel elements are mechanically supported via respective top end heads anchored to supporting structures and can be operated via handling machines.

Abstract: This bottom end-piece includes nozzles for directing the flow of water of the reactor along the lower ends of the fuel rods, the nozzles being arranged at nodes of the substantially regular network of the fuel rods, and an anti-debris device which delimits water flow channels. At least some of the water flow channels are arranged at nodes of the substantially regular network. Direction nozzles are arranged at least partially in the channels in order to delimit water passages therewith, and at least one water passage includes a first section and a second section which are mutually offset radially relative to the corresponding node of the network in order to form a baffle.

Abstract: Disclosed embodiments include fuel ducts, fuel assemblies, methods of making fuel ducts, methods of making a fuel assembly, and methods of using a fuel assembly.

Abstract: Nuclear fuel rods have cladding or fuel with physical parameters that substantially change based on axial position within a rod. Parameters include inner and outer cladding and fuel diameters or widths, volume, mass, internal volume, thickness, rod width, etc. Parameters are selected and implemented based on calculated operating conditions and/or desired fuel response at an axial position across an entire rod length and/or fuel assembly position, including both fueled regions and non-fueled zones. Desired parameters can be achieved through fabrication or later alterations. Parameter variations versus axial position and fuel assembly position are intentional and achieve desired fuel properties and responses, such as optimized fuel mass, pressure drop, over-pressurization protection, etc. Fuel rods can be compatible with existing fuel types and replace conventional fuel rods therein.

Abstract: The geometric dimensions and shape of a device for removing solid particles from the cooling medium that is circulated in the primary circuit of a nuclear reactor, in particular a boiling water nuclear reactor, are such that the device can be inserted in lieu of a fuel element or fuel assembly into an empty fuel element or assembly position of the reactor core of the nuclear reactor.

Abstract: The invention concerns a method comprising measurement on a fuel channel (14) of fuel assemblies (8) for nuclear boiling water reactors. The method comprises that: the measurement is done by the use of a non-destructive inductive eddy current measurement method, the measurement is done on a fuel channel (14) which has been used at least a certain time during operation in the core of a nuclear boiling water reactor, the measurement is done when the fuel channel (14) is located in water, the measurement is done on different places on the fuel channel (14), wherein through the method at least the hydride content of the fuel channel (14) at said places is determined. The method can be used in order to find out how shadow corrosion from a neighboring control rod influences the properties of the fuel channel (14).

Abstract: A precursor formulation of a silicon carbide material that includes a ceramic material and a boron-11 compound. The ceramic material may include silicon and carbon and, optionally, oxygen, nitrogen, titanium, zirconium, aluminum, or mixtures thereof. The boron-11 compound may be a boron-11 isotope of boron oxide, boron hydride, boron hydroxide, boron carbide, boron nitride, boron trichloride, boron trifluoride, boron metal, or mixtures thereof. A material for use in a nuclear reactor component is also disclosed, as are such components, as well as a method of producing the material.

Abstract: A spacer grid for nuclear fuel rods includes a plurality of unit spacer grids stacked one on top of another. Each unit spacer grid includes a plurality of unit spacer grid straps disposed at regular intervals in a row, and a plurality of fixing grid straps connected to respective opposite ends of the unit spacer grid straps so as to fix the unit spacer grid straps. Each unit spacer grid strap has convexities alternating with each other on opposite sides thereof at regular intervals, and at least one of the convexities has a diameter greater than the others. The unit spacer grids are rotated in one direction by a 90 or 180 degree angle when being stacked.

Abstract: A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.

Abstract: Fuel elements are supported by fuel assemblies configured for use in land-based nuclear reactors such as the VVER-1000. The fuel elements include a kernel having a multi-lobed profile that forms spiral ribs that include fissionable material (e.g., uranium or plutonium), a central metal displacer extending along a longitudinal axis of the kernel, and a metal cladding (e.g., zirconium and/or other refractory metals) enclosing the kernel. The fuel element may be fabricated by joint extrusion of the displacer, kernel, and cladding through a die to metallurgically bond the kernel and cladding.

Abstract: An assembly of the type having a water channel extending along a longitudinal axis and having an upper section of larger cross-section area than a lower section and at least one fuel rod receiving groove extending longitudinally on the outer surface of the lower section, fuel rods extending longitudinally and disposed around the water channel and fixing members for fixing at least one fuel rod to the water channel in the at least one groove below the upper section. According to one aspect of the invention, the at least one groove extends along the upper section such that a fuel rod received in fixing members is longitudinally extractable or insertable from the upper end side of the fuel assembly.

Abstract: A spacer grid for a nuclear fuel assembly for a light water reactor delimits a substantially regular array of cells housing nuclear fuel rods. The spacer grid further including supporting members which project into the cells from the peripheral belt of walls. The inner surface of at least one supporting member has before irradiation a concave shape in a plane transverse to the longitudinal direction. The inner surface of the contact part of the supporting member also has a convex shape in a longitudinal plane orientated radially with respect to the central axis of the corresponding cell before irradiation.

Abstract: A neutron source rodlet assembly having a separate source capsule assembly that is not encapsulated within the neutron source rodlet assembly. The neutron source rodlet assembly is made up, at least in part, of a neutron source positioning rodlet assembly and the source capsule assembly configured such that assembly together is feasible at a remote site and they can be shipped separately. The source capsule assembly has outer and inner capsules with the outer capsule having a threaded stud at one end that mates with a complimentary threaded recess on the neutron source positioning rodlet assembly. The inner capsule contains a neutron source. The neutron source positioning rodlet assembly and the source capsule assembly are locked together at their interface when the threaded joint is completely tightened. A secondary neutron source material may also be encapsulated within a hollow portion of the neutron source positioning rodlet assembly.

Abstract: A 12×12 fully ceramic micro-encapsulated fuel assembly for a light water nuclear reactor includes a set of FCM fuel rods bundled in a square matrix arrangement. The fully ceramic micro-encapsulated fuel is comprised of tristructural-isotropic particles. Each tristructural-isotropic particle has a kernel that is comprised uranium nitride. The kernel diameter is 400 or more micrometers. The fully ceramic micro-encapsulated fuel is further mixed with a burnable poison material.

Abstract: A boiling water reactor has a core disposed in the reactor pressure vessel and loaded with a plurality of fuel assemblies including transuranic nuclides. A ratio of Pu-239 in all of the transuranic nuclides included in the fuel assembly, which is loaded in the core, with a burnup of 0 is 3% or more but 45% or less. In the fuel assembly having a channel box and a plurality of fuel rods disposed in the channel box, a transverse cross section of a fuel pellet in the fuel rod occupies 30% or more but 55% or less of a transverse cross section of a unit fuel rod lattice in the channel box.

Abstract: In various embodiments, a spacer grid for a nuclear reactor fuel bundle is provided. The grid includes a plurality of interstitial dividers that form an array of cells. Each cell is structured to retain a respective one of a plurality of fuel rods to thereby form an array of equally spaced fuel rods. The grid additionally includes a perimeter band that peripherally surrounds the dividers and is connected to opposing ends of each divider. The perimeter band includes a plurality of spring tabs formed along and extending from an edge of the perimeter band. The spring tabs extend from the edge at an angle away from the dividers such that a distal end of each spring tab will contact an interior surface of a respective one of a plurality of walls of a channel in which the arrayed fuel rods can be inserted to form the fuel bundle.

Abstract: A method for design of a fuel assembly for nuclear reactors, including structural components made from zirconium alloy: the mean uniaxial tensile or compressive stress to which the components are subjected during the assembly life is calculated, the zirconium alloy of which the components are made is selected according to the following criteria: those components subjected to an axial or transverse compressive stress of between ?10 et ?20 MPa are made from an alloy with a content of Sn between Sn=(=0.025??0.25)% and Sn=?0.05?%: those components subjected to such a stress of between 0 et ?10 MPa are made from an alloy the Sn content of which is between Sn=traces and Sn=(0.05?+1)%: those components subjected to such a stress of between 0 and +10 MPa are made from an alloy the Sn content of which is between Sn=0.05% and Sn=(0.07?+1)%: and those components subjected to such a stress of between +10 and +20 MPa are made from an alloy the content of SN of which is between 0.05% and 1.70%.

Abstract: A fuel assembly for a light water reactor contains a fuel rod cluster and a spacer that has a number of cells, bounded by webs for laterally holding fuel rods. A damaged region including at least one damaged cell is present in an edge region of a spacer. There being fastened above or below the damaged region on the spacer with the aid of at least one connecting part is a replacement assembly that contains at least a number of cells that corresponds to the number of the damaged cells, at least a portion of the cells being traversed by fuel rods. A method for repairing the light water reactor fuel assembly in the case of which fixed above or below the damaged region on the spacer is a replacement assembly that takes over the holding function at least of one defective cell.

Abstract: Example embodiments are directed to fuel assembly components and nuclear fuel bundles including the fuel assembly components. Example embodiments of a fuel assembly component may include a cylindrical device having first and second ends and a mounting assembly on the first end of the cylindrical device configured to attach to and detach from a partial length fuel rod. Example embodiments of a nuclear fuel bundle may include an upper tie plate, a lower tie plate, at least one full-length fuel rod, at least one partial length fuel rod, and a fuel assembly component.

Abstract: Example embodiments are directed to upper tie plates for debris mitigation and fuel bundles that use the upper tie plates. Example embodiment tie plates may include a plurality of debris capture elements that overlap each other so as to create debris traps for particulate debris that would fall onto the fuel bundle. Example embodiment fuel bundles may use the upper tie plates for debris mitigation.

Abstract: Example embodiment fuel bundles use multiple types of spacers within the same fuel bundle. The type for each spacer location may be determined based on the axial position of the spacer, the characteristics of the spacer type, and the location and coolant characteristics for the particular example fuel bundle including the spacers. Historic performance data for the particular bundle location, predictive modeling, etc. may be used to determine what spacer types at which locations result in the best operating conditions and margins for example fuel bundles.

Abstract: A fuel element for a nuclear reactor has a fuel rod bundle, at least one spacer with cells defined by at least one web section made from a first material and several guide tubes each running through a cell and axially fixed thereto made from a second material. The first and second materials have differing thermal expansion coefficients. The connection between the guide tube and the spacer is embodied as follows: first and second projections are directly or indirectly fixed to the guide tube. The first projections are disposed in a first axial position and the second projections are arranged at a second axial position and the projections each engage in an opening through the web section to give an axially-acting undercut.

Abstract: A fully ceramic micro-encapsulated fuel assembly for a light water nuclear reactor includes a set of FCM fuel rods bundled in a square matrix arrangement. Fully ceramic micro-encapsulated fuel assemblies replace standard reference solid fuel assemblies with smaller number of FCM fuel rods that have a larger diameter than the diameter of the solid standard reference fuel rods, while keeping similar amounts of fissile material in the fuel assembly and maintaining comparable rates of burnup and number of EFPDs, and compatible power production, heat transfer and thermo-hydraulic features. A fully ceramic micro-encapsulated fuel rod includes multiple fully ceramic micro-encapsulated fuel pellets, which are comprised of tristructural-isotropic particles. In order to obtain compatible burnup rates with the standard reference fuel, the tristructural-isotropic particles have preferentially large diameter and packing fraction.

Abstract: The nuclear fuel assembly means a group of nuclear fuel rods disposed in a substantially regular array together with a support skeleton (5), the assembly having: two nozzles; guide tubes interconnecting the nozzles; and spacer grids secured to the guide tubes for holding the rods. The assembly includes at least one support skeleton reinforcing device disposed between two successive spacer grids and secured to guide tubes. The reinforcing device is disposed inside the group of rods and presents a transverse extent that is smaller than the transverse extent of the array of nuclear fuel rods.

Abstract: A fuel assembly may include a channel nosepiece; a lower tie plate positioned above the channel nosepiece; and at least one bundle retention clip connected to the channel nosepiece and the lower tie plate and configured to resist movement of the lower tie plate away from the channel nosepiece.

Abstract: The invention refers to a fuel assembly comprising a lower end structure, an upper end structure including a top nozzle (5), a plurality of fuel rods and a plurality of guide thimbles (3). The top nozzle includes a passageway and an annular groove (10) in said passageway. A sleeve (11) is provided for attaching the guide thimble (3) to the top nozzle (5). The sleeve has at least three slots (12) and includes at least three bulges (13). Each bulge (13) has two ends and extends between two of the slots (12). At least one of the ends of the bulge (13) extends to a position at a distance (d) from the respective slot (12). The invention also refers to a guide thimble device (9) for use in a fuel assembly.

Abstract: A nuclear fuel assembly support grid formed from an array of a plurality of orthogonally arranged straps in an egg-crate configuration with angled trailing and/or leading edges that are designed to break the correlation of vortices shed from the edges of the grid straps by varying the phase of the vortices to avoid resonant vibration of the straps.

Abstract: A ratio of the number of fuel assemblies loaded on a core to the number of control rod drive mechanisms is 3 or more. The fuel assembly itself contains mixed oxides of a low enrichment concentration uranium oxide containing 3 to 8 wt % in the average enrichment concentration of the fuel assembly, or mixed oxide containing not less than 2 wt %, but less than 6 wt % in the average enrichment concentration of fissile plutonium of. In the burner type BWR core on which the fuel assemblies are loaded, an average weight density of uranium, plutonium and minor actinides is 2.1 to 3.4 kg/L as a conversion at the value of unburned state.

Abstract: A fuel assembly for a pressurized water nuclear reactor contains a multiplicity of fuel rods which are guided in a plurality of axially spaced spacers which in each case form a square grid, composed of grid webs, with a multiplicity of cells arranged in rows and columns. In each case one control rod guide tube is guided through a number of these cells. At least one spacer is configured to be mechanically stronger in a first partial region than in a second partial region. In this second partial region, the spacer is provided with at least one resisting element which protrudes into a flow sub-channel formed between the fuel rods and increases the flow resistance. The resisting element counteracts a reduction associated with the mechanically weaker configuration, in the flow resistance in the second partial region and in this manner effects a homogenization of the hydraulic behavior of a spacer which is mechanically inhomogeneous on account of the varying mechanical configuration.

Abstract: Disclosed is a spacer grid assembly with mixing vanes supporting fuel rods of nuclear fuel assemblies and mixing coolant that flows around the fuel rods, and more particularly, a spacer grid equipped with mixing vanes that mix coolant flowing around fuel rods. The spacer grid with hydraulically balanced mixing vane patterns, in the spacer grid equipped with a strip dividing a plurality of unit grid cells and a plurality of springs, protruded in uniform directions of vertical and horizontal directions on a grid surface of the strip and supporting nuclear fuel rods, which includes: a plurality of mixing vanes protruded to the downstream of coolant on an upper end of the inner grid surface, wherein positions and directions of the mixing vanes are formed in regular patterns on the spacer grid. Thus, it can minimize coolant flow induced vibration of the spacer grid by balancing hydraulic load generated by the mixing vanes, around the center of the spacer grids.